Oscilloscope wave expansion



3 SheebS-Sheeh l l Inventor Joseph L. Tmsaah9 VERT/AL AMPLIFIER J. L. THElsEN OSCILLOSCOPE WAVE EXPANSION Filed Jux'xe 30, 1942 TVME TINE

SE L E C THR F0 TEN TIPHET May 7, 194e.

' PHASE .sw/F rms suffi-R May 7, V194.6., .1. Lf THEISEN oscILLoscoPE WAVE EXPANSION File@ June so. 1942 3 sheets-sheet s Ihvebor Joseph L.. Theis'en,

His Attorneg Paiente'd 2,399,955 l osornnoseorls wave ANsroN Joseph L. Theisen, Marblehead, Mass., assignor to .General Electric Company, a corporation of New York Application Junel30, i942, Serial No. 449,077,

Claims.

to a signal wave to be examined in the oscilloscope and for deflecting the beam in a transverse plane in response to a time-axis or -sweep wave.

It is an object of my invention to provide methods and apparatus for expanding on the screen of the oscilloscope an image of a portion of the signal wave to be observed, and for selecting any. desired portion of the signal wave for expansion.

It is a more speciiic object of my invention to provide methods and apparatus for modifying the shape of the sweep wave of the oscilloscope and to introduce a portion of` greatersteepness for expansion of the wave.

Other and further objects and advantages will become apparent as the description proceeds.

For convenience and simplicity the invention is described in connection with cathode ray oscilloscopes having deilection plates for electrostatic deection of thebeam. However, my invention is not limited to this particular form of apparatus.

In carrying out my invention in its preferred form I utilize discharge tube circuits for producing a sweep wave for application to the sweep def lection plates of the oscilloscope. The basic portion of the sweep-wave circuit may be similar to the basic portion of sweep-wave circuits devised by others, e. g. such as disclosed in the copending applications of Ellsworth D. Cook, Serial No. 338,360, led Junel, 1940, and Harris A. Thompson, Serial No. 350,409, illed August 3, 1940, both assigned to the same assignee as the present application. However, I produce expansionof the wave by greatly amplifying thenormal triangular or sawtooth wave of the conventional sweepwave circuit, so that but a small portion of. the ampliiled waverepresents full deilectlon in the direction of the time axis of the oscilloscope screen which is usually the horizontal axis. In

orderto prevent the cathode ray beam from striking the sidesot the tube or the anode plates and thus overloading the beam-energizing cirfcuit, I provide means for suppressing theportion of the sweep wave beyond that utilized for producing full scale deflection of the cathode nay beam. For this purpose 1 may either out oir the excess portion of the sweep wave or suppress the beam itself during the unwanted portions of the sweep wave. Theslgnai wave, the shape of which is to be represented on the cathode ray screen, is applied to signal deflection producing or vertical vdeflection plates of the cathode ray tube. For selecting the-portion of the signal wave which is to be expanded or spread across the cathode ray screen, I provide -a phase-shifting circuit arranged to select the portion of the high speed sweep wave applied to the horizontal plates.

My invention will be understood more readily from the following detailed description when considered in connection with the accompanying V In the drawings Fig. 1 is a graph illustrating a signal wave to be examined in the oscilloscope,

- shown as a sine wave by Way of example, and

illustrating the effect of expansion of a selected portion of a signal wave; Fig. 2 is a graph illustrating sawtooth sweep waves, one oi suicient magnitude to sweep the oscilloscope beam completely along the time axis in the course of a single cycle and the other greatly amplified for speeding upthe sweep wave and producing expansion of a selected portion of the signal wave;` Fig. 3 is a block diagram schematically representing a sweep Wave circuit which constitutes one embodiment of my invention; and which represents diagrammatically the shapes of waves appeering in various portions of the circuit; Fig. 4

is a circuit diagram schematically representing actual electric circuits and elements of the apparatusrepresented by the rectangles captioned Amplifler, Double ended blanking circuit,

and Expansion selector in Fig. 3; Figs. 5 and 6 are schematic diagrams partially representing an oscilloscope tube in perspective for the purpose of illustrating the principle of operation of the apparatus; Figs. '7 and 8 are diagrams furportional Vto it, and applying such voltage, as a i' synchronizing voltage, te input terminals of the sweep-wave circuit. Accordingly, a pair of syn- -wave I provide an amplifier I1, the input of which is connected to the output side of the sawtooth circuit I6. In addition I provide an arrangement 23 for selecting the portion of the signal wave to be expanded, and I provide a blanking circuit 45. The amount of horizontal expansion obtained may be made adjustable by providing for adjustment of the amplitude of the sweep signal. For

example, the amplier I1 may be provided with al gain control I1'. In the arrangement illustrated the output of the ampliiier circuit I1 is applied to a pair of electrostatic deflection plates I9 of a cathode ray tube and the sweep wave is a voltage wave. However, my invention is not limited to use with oscillographic devices of the type having electrostatic sweep instead of electromagnetic sweep, for example, wherein deilection coils are used carrying a current wave of correspending wave-form. 'Ihe plates I9 are those for prcducing'dedection ofthe cathode ray beam along the time axis or sweep axis and are referred to for convenience as the horizontal deflection plates, since the time axis is usually horizontal. The input signal I2 is applied to vertical deflection plates 2l of the cathode ray tube 20 usually through a, vertical amplier 22. For, in effect, shifting the phase ,relationship between the acting portion ofthe sweep wave and the signal wave to be examined, I provide the arrangement 23 for selecting the portion of the amplified sweep wave which occurs between the horizontal deflection plates I9. This arrangement may take the form of an adjustable voltage source for superimposing a potential difference on the horizontal deflection v plates and shifting the zero of the time axis in one direction or the other, even beyond the oscilloscope screen, the sweep-wave having been amn plied to such an extent that the entire horizontal length of the oscilloscope screen represents but a small part of the sweep wave. 'This source (Figs. 4 and 5) may comprise a potentiometer resistor 24, connected across a source of direct current 25, with a xed mid terminal 26 and an adjustable tap 21, the terminals 28 and 21 being connected to a pair of conductors 28 and 29, respectively, adapted to be interposed in the output circuit of the amplifier I1. The buffer I 4 consists of a suitable amplifier circuit of a type well known to those skilled in the radio frequency art.

The sawtooth circuit I6 is a conventional circuit for producing a sawtooth wave of the shape shown by the curve 8l, having a rising portion 8Ia and a ily-back portion 8Ib (Figs. 2 and 4)'.

After passing through'the amplifier I1 the saw-1 tooth triangular wave 3l appears in a greatly amplliied form as represented schematically at 82 in which the rising portion 88 of the wave 3a is greatly increased in slope for rapidly sweeping the cathode ray beam across the screen of the tube. It will be understood of course that Vthe curves 8| and 82 are simply schematic and are f not intended to'represent the actual or most the entire wave, corresponding to a sweep voltagel value designated M represents full horizontal defiection of the cathode ray beam. In order to prevent injury to the tube or overloading. which would occur from allowing the beam to be driven against the side of the tube or against the deection plates I9, the blanking circuit 45 is provided for the purpose of cutting off the cathode ray beam of the oscilloscope tube 25 when the sweep vwave 32 deviates in voltage an amount represented by the distance M corresponding to the fuli scale deiiection across the oscilloscope screen along the horizontal or time axis. The amplifier Il may consist of one or more vacuum tube. stages with a voltage tapped from one of the stages to operate the blanking circuit 45. The arrangement may be such as that illustrated in Fig. 4, for example, in which a doubletriode vacuum tube 46 is provided to serve as the last two stages of the amplifier I1. Two triode vacuum tubes 41 and 41' serve as the controlling elements of the blanking circuit 45.

The tube 46 comprises a pair of anodes 48 and 49 to which a source of anode4 voltage 50 is connected through a pair of anode resistors 5I and 52, the mid points of which are grounded through ripple-absorbing condensers. There is a common cathode 53 which is grounded, and there are grids or control electrodesv 54 and 55 associated with the anodes 48 and 49 respectively. The grid 54 is capacitatively coupled to the output of the pre vious stage of the amplifier or, if the amplifier consists of only two stages,- to the conductor 56, to which the positive output of the sawtooth circuit I6 is connected. The grid 55 is capacitatively coupled to the anode 48 in accordance with the well-known resistance capacity amplifier coupling. The amplifier output appears at the anode 49 and is applied through a conductor 29, and through that part of a potentiometer 24 which is between parts 26 and 21, to one of the horizon-tal deflection plates I9 of the cathode ray tube 20. It will be understood that the other horizontal deiiection plate is either grounded or held at a ilxed potential by a suitable device such as a potentiometer in accordance with the well-known cathode ray oscilloscope practice.

In order to suppress the cathode ray oscilloscope beam when the voltage of the sweep wave 32 deviates an amount corresponding to full scale deiiection across the oscilloscope screen, the control electrode or grid 58 of the oscilloscope tube 20 is connected through a conductor 59 to the corresponding elements designated by primed numbers.

The discharge tube,41 may advantageously be la vacuum tube of the type having a sharp upward bend in the characteristic curve representing the relationship between its anode current plotted along a vertical axis and its grid Vvoltage plotted along a horizontal axis. The grid 6I`is capacitatively coupled to the output terminal of the amplifier I 1, which is the anode 49 of the tube 46. In order to cause the blanking tube 41 to operate near the bend in its characteristic curve, an adjustable negative ybias is applied thereto. lThis may take the form of a potentiometer 88iconnected across a voltage source 54 connected on the positive side to the cathode 82. In order that the blanking tube 41 may supply an adequate negative potential at proper times, its cathode 62 is held negative with respect to the cathode 85 of the cathode ray oscilloscope tube 20. The cathode $2, for example, may be -connected to the negative side of a voltage source 8d' grounded in the positive side, the oscilloscope cathode 65 being grounded, The blanking-tube anode 60 is connected lto the positive side of a source of anode voltage, such as the source 50, through an anode resistor 56 which also has its mid-point bypassed through a ripple-absorbing condenser connected to ground. The constants of the circuits, the characteristics of the tube d1 and the bias voltage provided by the grid bias potentiometer B3 are so chosen as to cause the blanking tube 61 to become strongly conducting, when the voltage of the wave 32 appearing at the amplifier anode 39 rises an amount represented by the distance M. (Fig. 2.) Since :the tube B1 is one having the aforesaid sharp bend characteristic, as longI as the sweep-wave voltage applied to the grid 6l remains below the value M, the anode current of the tube 41 is negligible and a positive voltage is maintained on :the cathode ray oscilloscope grid 58. However, when the sweep-wave voltage rises more than the value M, the bend in thecharacteristic curve of the tube d1 is passed and a relatively heavy discharge current `flows through the tube 31 causing a large voltage drop in the anode resistor 66, depressing the voltage of the oscilloscope grid 58 below that of the oscilloscope cathode -65 and cutting 0E the cathode ray beam to suppress the wave traced on the screen.

It will be understood that suitable means, adjustable if desired,are ordinarily provided for normally maintaining the potential of the oscilloscope grid 58 at the value which produces the most satisfactory operation. This may take the form of a voltage divider, for example. Such a voltage divider is represented in Fig. 4 by the vanode resistor 66 and a rheostat 61 of suitable value connected between the anode 6G and ground. Thus normally the potential of the oscilloscope grid 58 is iixed by the ratio between the resistance of the rheostat 61 and the resistance 68 which are connected in series to the voltage source 50. However, when the blanking tube 31 becomes strongly conducting it draws current of such magnitude through the anode resistor 38- blanking tube 41 drops abruptly along the line 1@ but remains strongly negative with respect to the oscilloscope 65 until the sweep voltage falls again by the amount M. The exact shape of the negative portion 1I of the curve 68 will of course depend on the characteristics of the tube 41.

The blanking tube 1' is connected in a manner similar to the tube 41, except for its input connection. For the purpose of making the tube 51 act when thesweep wave voltage falls more than` a predetermined amount instead of when it rises, a suitable inversion circuit or phase inverter is interposed between the anode 49 of the ampliner tube 46 and the control electrode 6l of the blanking tube A1'.

The phase invertermay take the.f orm of a vacuum tube 30 having suitable internal and circuit constants for forming a conventional nonamplifying phase inverter. For example, as i1- lustrated it has a control electrode 13, resistance capacity coupled to the anode '39 of the amplifier tube 46 and has an anode 14 to which the control electrode 6l of the blanking tube d1' is resistance capacity coupled. y

The arrangement 23, for selecting the portion of the signal wave to be examined serves to shift the eiective zero of the time axis back and forth according to the portion of the si-gnal wave to be expanded. Accordingly means are provided for adjusting the blanking circuits to cause the oscilloscope beam to be cut oi when the beam approaches either end of the actual time axis of the oscilloscope screen. Preferably the arrangement is such that adjustment of the blanking circuits is changed automatically as the device 23 is adjusted for selecting diiferent portions of the signal wave for expansion. For example, as illustrated in Fig. 4 a potentiometer 15 maybe provided for increasing the negative bias of the control grid of the blanking tube 41, when the device 23 is operated to shift the effective zero of the time axis to the left from an extreme right-hand position. Similarly, an oppositely arranged potentiometer 1S is provided for increasing the negative bias 'of the control grid of the blanking tube 41 when the device 23 is operated to shift the effective zero of the time axis of the oscilloscope to g the right from the extreme left-hand position.

The potentiometers 15 and 16' may consist of direct current sources 11 and 18 across which potentiometer resistors 19 and 80 are connected having sliding taps 8i and 82 respectively. The expansion selector arrangement 23 has-a corresponding sliding tap 21 cooperating with the potentiometer resistor 24 as previously mentioned. The three sliding taps 8l, 82 and 21 are connected to a common operating member shown in Fig. 4, such as a bar 86, which is connected to'a pointer 86 and which cooperates with a scale 81.

It will be observed that the right-hand end of the potentiometer resistor 19 and the left-hand end of the potentiometer resistor 80.1l are connected to the positive terminals of the sources 11 and 18 respectively andare both connected by a conductor 88 to the tap 63' of the potentiometer E3 which serves as the negative end of either ofv the control grid circuits of the tubes t1 andd1'. The sliding tap 8i is connected to the control grid 6i of the tube d1 and similarly the sliding tap 82 is connected to the control grid 6I' of the blanking tube 41'. Thus the blanking tube ad- `iusters 15 and 13 vary the control grid bias of the blanking tubes 61 and B1 oppositely as the arm 85 is moved in one direction or the other for adjusting the device 23 to select the portion of the signal wave to be expanded.

The manner in winch the device 23 operates to select the portion of the signal wave t'o be expanded may be observed from a consideration of Athe simplied diagrams '5 and 6. Let it be assumed first 'that the amplifier I1 of Fig. 3 is omitted. The magnitude of the voltage deviation produced by the sawtooth circuit I6 is pre- Opercreased sweep speed. It would tend to move through a greatly increased angle from the points A' to B' if the construction and arrangement of the oscilloscope tube 20 permitted such a wide sweep angle. However, the points A' and B are merely hypothetical for the purpose of explanation. The magnitude of the voltage source 25 is so chosen that the movement of the sliding tap 21 back and forth along the potentiometer 24 between the limits of movement a and b would also tendto produce deflection of the oscilloscope beam between the hypothetical limits A', and B. Fig. shows a simplied circuit with only the expansion selector arrangement 23 in the horizontal deection circuit, and Fig. 6 shows only the horizontal sweep I1 in the horizontal deflection circuit.

As shown in Fig. 4, the voltages of the devices i1 and 23 are in series. Then as illustrated in. Fig. l the oscilloscope beam still tends to sweep back and forth between the hypothetical limit points A' and B', but the 'hypothetical zero or center of the time scale is shifted to the left if the tap 21 of the device 23 is shifted to the left. Actually the oscilloscope beam can move only from one end to the other of the horlzontalaxis of the screen and only a portion cd of the hypothetical range AB' is actually effective. Thus the portion of the signal wave cd occurring between the points c and d of the hypothetical time axis is produced in greatly expanded form (Figs. 1 and 7). If the sliding tap 21 of'the expansion selectin-g device 23 is moved to the right instead of to the left, the hypothetical zero or center of .the range A', B is shifted to the right and only the portion of the hypothetical range between the f points e and f is effective for deiiecting the oscilloscope beam. Accordingly the portion of the siglnal wave occurring during the interval e, is

produced on the oscilloscope screen in expanded form (Figs. l and 8). In order to prevent destruction of the tube, it is necessary to a provide a double-ended blanking circuit l5 for cutting ofi the oscilloscope beam whenever it approaches either end of the actual time axis of the oscilloscope screen 9. The manner in which this accomplished is illustrated in Fig. 2.

In Fig. 2 the output wave il of the sawtooth circuit le is plotted along the 1:, axis (sweep voltage is measured in a vertical direction and time in a longitudinal direction). This wave is amplified by the amplier i1 and appears as awave 32 plotted in Fig. 2 along the axis. The vertical distance M is the permissible deviationA in the sweep wave voltage corresponding to sweeping the beam from one end to the other of the actual oscilloscope horizontal axis;` for example, between the points A and B in Figs. 5 and 6, between c and d in Fig. 7 and between e and f in Fig. 8. In Fig. 2, for convenience. the height of the unamplified `sweep wave 3i is shown as equalling the distance M. It will be understood, however, that the actual maximum deviation of the unampliiled wave 3i does not necessarily bear any relation to the value M and length of the actual oscilloscope horizontal axis since in the apparatus illustrated the sweep wave Il is greatly amplified and only the ampliiled wave 22 is applied to the sweep plates for expansion If the adjustment tap 21 of the expansion selecting device 221s set at the mid point 2l of potentiometer 24. the hypothetical range A' or B' will be symmetrical with respect to the oscil- I loscope screen and only the portion between the ordinates g and I1. of the rising portion, 33 of the sweep wave will be eiective (Fig. 2). The ampliiled sweep wave 32 thenin effect has its axis shifted to the line xo, xo' shown in Fig. y2. Moving the adjustment tap 21 toward the right on the potentiometer 24 has the effect of shifting the horizontal axis or the sweep wave 32 to the line 3:1, im'. as illustrated'in Fig. 2. For this latter condition, as illustrated in Fig. 1, only the portion of the signal wave 89 between the points c and d on the time axis will be produced on the screen 9 and the sweep speed will be so great that this portion of the wave is greatly expanded to form a segment Sl.

Referring to Fig. 4 when the tap 21 is in the extreme right-hand position, the tap 8l is also in the extreme right-hand position and the potentiometer 1Q provides no supplementary bias to the control grid ti of the blanking tube 41. Consequently as soon as the sweep voltage appearing' at the anode t@ of the tube ES rises from its minimum value by an amount M, the tube 41 is caused to become conducting. its anode 8G becomes negative and the control grid 58 ofthe oscilloscope 28 likewise becomes negative and cuts of! the beam of the oscilloscope. if the taps Il and 21 are moved somewhat to the left for the purpose of selecting a different portion of the signal Y wave voltage has reached the magnitude represented by the point if in Fig. 2,- the adjusting device l5 of Fig. e is provided. This supplies additional negative bias corresponding to the negative voltage mtrcduced in the horizontal.

sweep circuit by the expansion selecting device 23;. Consequently the control grid ti of the blanking tube l does not reach the value required for cutting od the oscilloscope beam until the sweep wave voltage has reached the value .f represented in Fig. 2.

However, on the return sweep as soon as the sweep voltage falls below the value e illustrated' in Fig. 2, it will be necessary to cut ci the oscilloscope beam to avoid destruction of the oscilloscopetube 28. This is accomplished by the blanking tube I1' and its adjuster 18. Since the inversion circuit n is interposed in advance of the tube 41', it operates on a falling sweep voltage instead of a rising sweep voltage. With the tap l2 at the extreme lett-hand position. that is, at the positive end of the potentiometer resistor il, the blanking tube 41' operates when the sweep voltage has fallen from its maximum value by an amount M. With the taps Il,

. l2 and 21 in the position shown in Fig. 4 nearly all l'le of the negative bias of the potentiometer Il is inserted in the control grid circuit of the blanking'tube 41' the blankingtube becomes opasaaexsrsm resents the voltage required to sweep the beam from one end to the other of the horizontal axis of the oscilloscope screen 9. Furthermore, since the taps 8|, 82 and 21 are ganged, the operation of the blanking tubeA adjusters I and 'I0 is synchronized with the operation of the device 23 for selecting the operation of the signal wave to be expanded and the oscilloscope beam is blanked out except during the interval of time that it is impinging on the screen.

If desired a blanking circuit may be provided which is directly responsive to the voltages on the horizontal or time sweep plates I9 and which becomes eiective in response to excessive voltage on either ofthe horizontal sweep plates. For example, an arrangement may be employed such as shown in Fig. 9 which has the advantage of gauging fewer potentiometers than in the ar' rangement shown in Fig. 4.

In the arrangement of Fig. 9 a horizontal circuit of the tubes 46A and 66B is shown. The

anodes 9| and 92 of the tubes 46A and 06B are coupled through condensers S3 and 90 to the horizontal sweep plates, designated in Fig. 9 as ISA and I9B, respectively. Resistors 95 and 9B are connected in series between the plates ISA and I9B and have a common terminal 91 which is grounded. In this manner variations in the voltage output of the amplifier Il produce oppo` site variations in potential with respect to ground on the horizontal sweep plates |9A and I9B. As in the arrangement represented by Figs. 3 and 4 the amplitude of the (output of the amplifier I'| is made considerably greater than that required to sweep the oscilloscope beam the length of the horizontal axis of its screen for the purpose of increasing the speed of the horizontal sweep wave and causing the selected portion of the signal wave to be expanded.

In order to change the eiective center point of the horizontal sweep wave and thereby select the portion of the signal wave which is to be examined, a potentiometer arrangement is provided for supplying adjustable supplementary voltage to the horizontal sweep plates ISA and I 9B. 'As illustrated in Fig. 9, this takes the form of a double potentiometer consisting of a pair of resistors 98 and 99 connected in parallel across a voltage source consisting of a battery 25 and `having a pair of ganged or mechanically connected taps |00 and |02 which move along thev resistors 98 and 99, respectively, in unison. The resistors 98 and 99 are so connected and positioned that the potentials on the taps I0| and |02 vary in opposite directions as the taps are moved in one direction or the other. The taps |0| and |02 are electrically connected to the horizontal sweep plates IBA and I9B, respectively.

For extinguishing the oscilloscope beam when the voltage on either sweep plate |9A or I9B reaches a limit beyond which the beam would be deected too far toward the ends ofthe horithe side walls of the cathode ray oscilloscope 20, a blanking circuit is provided represented by twin tube |03. The blanking circuit is so conzontal axis of the screen, that is, too far toward nected that it is directly responsive to voltages on the horizontal sweep plates |9A and -JB and no mechanical connection or ganging with the expansion selector potentiometer 98-99 is required. The blanking circuit utilizes Aan electric discharge device which may take the form of a twin triode vacuum tube such as designated by the reference numeral |03. 'Ihe tube |03 includes a pair of anodes |00 and |05, a pair of control electrodes |08 and |01 and a common cathode |08'. Thus, one triode section is formed by the elements |04, |06 and |08; and the other triode section is formed by the triodes |05, |01 and |08.l The anodes |00 and |05 are connected to the positive terminal of the anode voltage source 50 through an anode resistor |09. A voltage divider for determining the potential of the oscilloscope control grid 58 is provided which consists of resistor ||0 and a rheostat G1 connected in series between the anodes |00, |05 and ground, the junction terminal of the resistor I I0 and the rheostat 61 being connected to the oscilloscope control electrode 58.

The blanking tube control electrodes |06 and |01 are connected to the oscilloscope horizontal sweep plates I9A and I9B, respectively, for caus- A effective until a ixed voltage limit is reached, an

initial bias is provided in the circuit of the blanking tube |03 by providing a source of voltage between the cathode |08 and the ground connection of the apparatus. For the purpose of adjusting the voltage limits the bias voltage may be made adjustable taking the form of a voltage source such as a battery III shunted by a potentiometer resistor ||2 having one end connected to ground and having an adjustable tap I I3 connected to the blanking tube cathode |08, A by-pass condenser H0 with proper capacityv for the frequencies involved is connected between the cathode and ground to avoid any degenerative eect from the cathode resistor IIE.

To provide control potential adjustment for the oscilloscope 20, its cathode 05 may be connected to a source of adjustable positive bias consisting of a battery'and potentiometer combination ||5 shunted by a by-pass condenser H0 of sufficient value for the frequencies Vinvolved.

It will be observed that the sweep wave voltage output produced by the amplifier I1 will appear on the horizontal sweep plates |9A and I9B of the oscilloscope and that the wave'may be shifted in one direction or the other from neutral or ground voltage by adjustment of the gang potentiometer taps |0| and |02,thereby selecting the portion of the signal wave which is expanded as previously explained in connection with Figs. 5 to 8, inclusive. AIf the voltage on *either of the sweep plates |9A or I9B exceeds the value for which the control electrodes are biased, one triode section of the tube |03 becomes strongly conductive and, accordingly, a large drop in potential takes place through the anode resistor |09 lowering the potential of the anodes |00 and |05. In consequence the potential of the oscilloscope control electrode 50 is lowered in relation tothe potential of its cathode v|55 rto such a value as to cut oil the oscilloscope beam .of the oscilloscope tube 20. Adjustment of the during expansion of the signal wave and blanking during the remainder of the signal wave is obtained by adjustment of the rheostat 61 and the oscilloscope bias potentiometer H5.

I have herein shown and particularly described certain embodiments of my invention and certain methods of operation embraced therein .for the purpose of explaining its practice and showing its application, but it will be obvious to those skilled in the art that many modifications and variations are possible, and I. aim therefore to cover all such modifications and variations as fall within the scope of my invention which are denned in the appendedclaims.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A signal wave expansion arrangement for a sweep wave circuit of an oscilloscopio device having a signal tracing beam, comprising in combination with a sawtooth Wave generator adapted to produce a sweep wave for generating a signal tracing beam along a sweep axis of the oscilloscopio device and spreading an image of the signal wave on. the screen of the oscilloscopio device, an amplifier f or increasing the amplitude of the sweep wave and thus increasing its slope to increase the speed of sweep and thereby expand the portion of the signal wave to be traced, a device for superimpos'ing an adjustable voltage on the output wave of the amplifier for selecting the portion of the sweep wave which is effective in deecting the beam within the limits of the time axis of the oscilloscope and a device, synchronized A with'said adjusting device responsive to voltage variations above and below the voltage deflecting the signal tracing beam to the permissible limits of the sweep axis, for preventing further sweep of the signal tracing beam.

2. An oscilloscopio sweep wave generator comprising generating means for producing a trianguiar wave adapted to be applied to one of the deection circuits of a cathode ray oscilloscope with a control grid and of greater peak value than required for full scale deilection, a device' for superlmposing an adjustable voltage on said triangular sweep wave for shifting the edective center oi the sweep axis in one direction or the other from the actual center of the oscilloscope, a blanking circuit responsive to rise and fall' oi the sweep wave beyond'predetermined limits having output terminals adapted to be connected t0 the grid circuit of said oscilloscope for applying a negative voltage therein of sufcient value to cut of! the cathode ray beam whenever the sweep wave deviates beyond said limits, said blanking circuit having adjusting mechanism interconnected with said first-mentioned adjusting device for shifting the voltage limits at which the blanking circuit cuts oiI the cathode ray beam whereby th'e oscilloscope-beam is cut oil when it deflects to the edge of the oscilloscope screen and the slope of the used portion of the sweep wave is caused to be relatively great to produce high speed sweep and expansion of the signal wave to be examined during apor- I. tion of the cycleofthe signal wave to be 'examined.

3. An oscilloscopio sweep wave generator comprising generator means for producing a. triangular voltage wave adapted to be applied to one of the deflection circuits of a cathode ray'oscilloscope with a control grid, but of greater peak value than required for full scale deflection. an adjustable device for superimposing a nxed value of voltage on said triangular wave for shifting the eiective center of the triangular wave with respect to the center of the cathode ray oscilloscope for rendering a predetermined portion of the triangular wave eilective in producing deflection of the cathode ray beam of the oscilloscope, a blanking circuit responsive to rise of the sweep wave above a, predetermined value and a. second blanking'circuit responsive to fall of the sweep wave below a predetermined value, said blanking circuits having a common output terminal adapted to be connected to the control electrode or grid circuit of the oscilloscope for applying a negative voltage therein of sufllcient value to cut oil! the cathode beam whenever the sweep wave deviates beyond said limits, a device interposed between said sweep wave generator and the first ol.' said blanking circuits for inserting an adjustable biasing voltage, a second device interposed between said sweep wave generator and said second blanking circuit for inserting a second adjustable voltage and an interconnecting device for adjusting the voltages of said last two adjustable devicesv in opposite directions simultaneously with the adjustment of said lrs't-mentioned adjustable device.

4. A signal wave expansion arrangement for a sweep wave circuit of an oscilloscopio device havlng a signal tracing beam comprimng in combination with a sawtooth generator adapted to produce a sweep wave voltage for generating a signal tracing beam along a sweep axis of the oscilloscopic device and spreading an image of the signal wave on the screen of the oscilloscopio device, an

ampliiler for increasing the amplitude of the sweep wave and thus increasing its slope to increase the speed of sweep and thereby expand the portion 0f the signal wave to be traced, a device for superimposing an adjustable voltage on the output wave of the amplifier for selecting the portion'of the sweep wave which is effective in deecting the beam within the limits ofthe time axis of the oscilloscope and a device responsive to voltages of the sweep wave exceeding predetermined limits for preventing further sweep of the signal tracing beam.

5. A sweep wave generator for a cathode ray oscilloscope having deflection circuits and a control grid, said generator comprising generating means for producing a sweep wave adapted to be applied to one of the deilection circuits of the cathode ray oscilloscope and of greater peak value than required for full scale deilection, and a the cathode ray beam whenever the sweep wave deviates beyond said limits, said blanking circuit having voltage responsive control elements for rendering the blanking circuit eilective in respouse to voltages of predetermined magnitudes,

said voltage responsive elements having a .pair oi!A connections to which the sweep wave is applied in opposite polarity relationships.

J. L. THEISEN. 

